It is well known in suspended ceiling systems to suspend ceiling panels from a grid of inverted T-beam support members. The inverted T-beam support members extend downwardly from a permanent ceiling structure, and enable the ceiling panels to be suspended therefrom in spaced relation to the permanent ceiling structure. The suspended ceiling panels are typically supported from the grid of inverted T-members in edge-to-edge relation to form a continuous ceiling which conceals the supporting grid and the permanent ceiling structure from view. Preferably, the suspended ceiling is spaced sufficiently from the permanent ceiling structure to allow utility structure, such as pipes, duct work, electrical wiring, etc., to be conveniently located in the space between the suspended ceiling panels and the permanent ceiling structure.
There are many techniques for attaching or suspending ceiling panels from a grid of inverted T-beam support members. Some of these techniques utilize clips or wires to attach and detach the panels from the support members. Other methods support the ceiling panels from the inverted T-beam support members by simply resting each panel on the T-beam support members. In such systems the ceiling panels can be readily displaced by manual upward movement of the panel toward the permanent ceiling structure and out of engagement with the grid.
Another method for suspending ceiling panels is set forth in U.S. Pat. No. 4,541,216. In this system each panel or pan is seated within an opening formed in the grid by the inverted T-beam support members. The pans are supported on the support members, and maintained in position by engagement with overhanging ribs of the support members.
In correctional institutions, and other facilities requiring increased security, it is preferable to provide a suspended ceiling system with ceiling panels which are secured within the grid and cannot be removed by upward manual movement of the panel. Although systems using techniques as in U.S. Pat. No. 4,541,216 may be more effective than some prior methods used in such secure environments, the pans used by the system are difficult to manufacture, and are able to be removed from the grid by prying actions. Such prying actions are able to successfully remove the panels by applying a lever under one wall of the panel, and, by a "zipper" effect, running the lever along the full length of one side wall of the panel. Upon removal of one side of the panel, the remaining sides of the panel may also be removed by similar prying actions.